1. Field of the Invention
The present invention relates in general to telecommunications networks, and more particularly, to handing off communications from a mobile station operating in one access system to the mobile station operating in another access system. This invention is particularly useful for handing off ongoing communication sessions from a mobile station operating in a public wireless network to the same mobile station operating in a private wireless system, after the mobile station registers in the private wireless network. This invention, however, is also particularly useful for handing off an ongoing communication session from a mobile station operating in a private wireless system to the same mobile station operating in the public wireless network, after registering the public wireless network.
2. Description of Related Art
Public wireless telecommunication networks have been developed using a model that is similar to traditional wireline telecommunication networks. Traditional wireline Telecommunications networks typically carry “signals,” as well as the voice or data comprising the conversation between the calling party and the called party. These signals monitor the status of the lines, indicate the arrival of incoming calls, and carry the information needed to route the voice or other data through the network. At one time, these signals were inband, i.e., the signals were transmitted through the same circuits as used for voice transmission. However, most circuit-switched telecommunications networks now use out-of-band signaling, i.e., the signals are transmitted over a signaling network separate from the circuit-switched network that carries voice and data. Thus, signals carried on the separate signaling network are used to control the switches in the circuit-switched network to set up and tear down the circuit between the calling party and called party.
In a typical public wireless networks, switching is performed by one or more mobile switching centers (MSCs). Each MSC typically controls one or more base stations or base transceiver stations (BTSs), sometimes via one or more base station controllers (BSCs). Each BTS provides a wireless coverage area within which mobile stations can communicate with the BTS over an air interface. The mobile stations can be cellular or PCS telephones, personal digital assistants (PDAs), and/or other devices. Different formats may be used for communicating over this wireless interface. At present, the most commonly used formats in the United States are Advanced Mobile Phone Service (AMPS), Time Division Multiple Access (TDMA), Global System for Mobile Communications (GSM), and Code Division Multiple Access (CDMA).
In addition to public wireline and wireless networks, businesses and other organizations (collectively referred to herein as “enterprises”) have been using private telecommunications networks for many years. Such networks are “private” in that the networks' coverage areas are more geographically limited, and typically, but not necessarily, subscription to the networks is limited to a select group of subscribers. For example, many enterprises have used private wireline switching systems, such as private branch exchanges (PBXs), to switch calls to and from telephones in the enterprise's office area. Such private telecommunications networks advantageously allow an enterprise greater control over its telecommunications system and enable the enterprise to customize the telecommunications it provides to its subscribers.
More recently, private telecommunications networks have also been provided with wireless capability. In particular, there have been developed various wireless office telephone systems (“WOTS”) that provide for wireless communication in a, typically, limited geographic area, such as a building or campus. See, e.g., Lawrence Hart, et al., “Cellular and PCS: The Big Picture,” p. 183–232 (1997). However, many such WOTS systems require specialized telephones, so that a standard cellular or PCS telephone that can be used in a public wireless network may not work in a given WOTS system. With many people routinely carrying a cellular or PCS telephone, requiring a different telephone to be used at work is a substantial inconvenience.
To overcome this disadvantage, some wireless office systems have been developed in accordance with the TIA's IS-94 specifications. The IS-94 specifications allow the same mobile stations to be used in both private and public wireless networks. However, IS-94 is not designed to hand-off calls between the private and public wireless networks. The lack of hand-off capability is a significant drawback. In particular, if a user moves out of the limited coverage area of the wireless office system during the course of a call, the call may be dropped. Alternatively, if the user during the course of a communication session moves into the coverage area of the private wireless network and a hand-off is not effectuated, the public wireless network may not realize savings of network resources that may have occurred had the communication session been handed-off.
In addition to the WOTS systems, recent advances in telecommunication services served over local area network, such as Voice-over-Packet-Data network communications, have provided the impetus for delivering wireless telecommunication services over local area networks. Accordingly, support for wireless telecommunications services over local area networks is approaching near necessity for many enterprises. And the need for such services is rapidly growing, not just for enterprises, but also for individuals for personal and business use in the home or home office, respectively. This need may be satisfied by a wireless local area network based on the Bluetooth specification, which is designed to serve telecommunication services to mobile stations operating within its coverage area. The Bluetooth specification provides that Bluetooth technology devices, such as PDAs and/or cell telephones, may quickly and reliably exchange data with other Bluetooth technology devices, as well as provide local wireless connectivity with the wireless local area network element, such as desktop and docked notebook computers. Like the WOTS specification, the Bluetooth specification is not designed to hand-off communications between public and private wireless networks.
Even more recently, the IEEE promulgated the IEEE 802.11 standards to define the communication protocols between mobile stations, and network access points that bridge mobile stations to a local area network. One major advantage of using a wireless local area network that conforms to the IEEE 802.11 standard is the ability to use freely-available, unlicensed spectrum, including the Industrial, Scientific, and Medical (ISM) band. Another advantage provided by the 802.11 standard is the specified support for the 1-Mps, 2-Mps, and the recently added 5.5-Mps and 11-Mps transmission speeds. In the near future, the IEEE standard may support transmission speeds of 36-Mps, 48-Mps, 54-Mps, and 108 Mps. While the IEEE 802.11 standard loosely defined a portal or bridge function, the portal or bridge function indicates how to perform a hand-off of an ongoing communication session engaged in by a mobile station in a local area network.
Some wireless office systems, however, have some limited ability to allow users to move between the private and public cellular networks during the course of an ongoing communication session. An example is the ROAMEO in-building wireless telephone system that is sold by AG Communication Systems, headquartered in Phoenix, Ariz. The ROAMEO system is provided as an adjunct to a company's existing PBX, Centrex, or key system and allows standard wireless telephones to act as wireless extensions of the existing office desktop telephones. If a user originates a communication session in the public wireless network, and then moves into the building served by the ROAMEO system during the course of the communication session, the session will continue using the public wireless network provided that the signal from the public wireless network is able to penetrate into the building. Moreover, once the communication session is ended, the telephone is automatically registered on the ROAMEO system. However, if a communication session is originated within the coverage area of the ROAMEO system, it may be dropped if the telephone leaves the ROAMEO coverage area.
Widergen, et al., U.S. Pat. No. 5,890,064 discloses a wireless office system that is said to be integrated into both a private telephony network and a public cellular system. Certain of the disclosed embodiments are said to support handover of ongoing communication session between cells of the wireless office system and the public cellular system. Analogous to the public wireless network, Widergen's wireless office system includes a wireless office gateway, and a radio access network to provide wireless communications to corporate mobile terminal, which is part of a corporate group of terminals of the private telephony network.
A disadvantage with this configuration, however, is that the wireless office system “is implemented as a private wireless system that operates according to the same standard as the public cellular system.” See Widergen, et al., In.1 col. 4. While such a system allows the subscriber to use the same mobile station in both the public wireless system and the wireless office system, it may be advantageous for subscribers to have one or more mobile stations that use different standards. Differing standards may take advantage of different range and power capacities for both the mobile station and subscribing networks, which may reduce or eliminate waste of network resources, and prevent over design of both types of networks. Widergen's technique of using the public wireless network elements to control the transmission of communication services in both the public and private wireless network does not facilitate application of different standards, either using a single mobile station or multiple stations.